Neutron irradiation degrades the reactor pressure vessel (RPV) steels. As the steel degrades, the mechanical properties of the material also change which affect the crack tip stress fields. In this article, we show that reduction of the “fracture toughness” of the RPV steels due to neutron irradiation can be interpreted by a change of an “equivalent constraint” due to material property changes. Using the J-A2 two-parameter fracture methodology to quantify the crack tip stress fields and a critical stress fracture criterion, the methodology is applied to the interpretation of fracture toughness test data from un-irradiated and irradiated RPV steels.

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